The present invention relates to a method and device for monitoring the steering performance of the operator of a vehicle and reacting to the detection of abnormalities to activate a warning signal and/or switching to an automatic steering mode. More particularly, the invention relates to a monitoring of the steering control system of a vehicle to produce a steering signal indicating the size and direction of steering deflections, analyzing such deflections to detect an abnormal steering performance and reacting to such performance to cause activation of such warning signal and/or switching to an automatic steering mode.
The development of modern combat aircraft with increasingly high demands on performance has in recent years created a situation where the mental and physical abilities of the pilot set the limits of total capability and performance. One of the problems is the risk that in certain extreme situations the pilot will be subjected to sudden loss of consciousness caused by an extreme increase in the load factor (acceleration). This condition, which among experts is usually called G-LOC (G-induced Loss of Consciousness), is closely related to the loss of consciousness that is known to occur to a combat aircraft pilot exposed to a high, evenly growing load factor, e.g., on climbing after a dive. However there is a distinct difference. In the last-mentioned situation warning symptoms appear such as tunnel vision or a still longer effect on the pilot's vision function (so-called "gray out"). As a result the pilot remains capable of interrupting a dangerous maneuver in time. In contrast G-LOC occurs instantaneously and without any sensation to forewarn the pilot. The difference depends on the level and the amount of time in which the change in load factor occurs.
Medically, the loss of consciousness that may occur to a pilot is directly related to the level of oxygen in the brain and thereby to the heart's ability to overcome the hydrostatic pressure difference between heart and brain. During a slow G-load increase the blood flow to the brain will decrease gradually in proportion to the increase of the counter-pressure in the heart. This in turn leads to a decrease of the oxygenation in the brain to a corresponding degree; this despite the fact that the body, through vasoconstriction and increased pumping ability, endeavors to compensate for the counter-pressure increase. The vision function is affected due to the low oxygen level before the level becomes so low that loss of consciousness occurs.
If, on the contrary, the blood flow to the brain is suddenly interrupted due to a rapid G-load increase, there remains only the brain's own oxygen reserve, which will last for about 5 seconds, whereupon loss of consciousness occurs without prior symptoms. Also there is insufficient time for the body to respond to the quick oxygen change to compensate through alteration in the blood pressure.
G-LOC causes a total loss of consciousness for about 15 seconds, whereupon there is a period of continuing serious lack of oxygen for about 10 seconds. During the last part of the loss of consciousness the pilot may be subjected to rapid muscle contractions similar to those occurring during an epileptic seizure. When consciousness is regained disorientation usually follows in combination with amnesia on awakening.
The load factor at which lack of oxygen begins to appear is about 6 G subject to individual variations. There may be danger of G-LOC if the load factor increases to a total of more than 6 G during a time shorter than 5 seconds and if this high load factor is allowed to act longer than 5 seconds.
Such values can easily be obtained in the latest generation of combat aircraft and G-LOC must therefore be regarded as a very serious problem both with respect to flying safety as well as effectiveness in a combat situation. Several crashes have recently occurred abroad with newly developed aircraft and in all cases G-LOC has been stated to be the direct cause. There is a finding that 20% of certain groups of military airmen in the USA have undergone G-LOC. This information underlines further the seriousness of the situation and the need for a solution to the problem.
It is previously known to provide the pilot with means for maintaining the brain's oxygenation above a critical level through direct physical effect on his body and it has been attempted to use such means as protection also against a rapid increase of the load factor. During some ten years of study of the problem by aeromedical experts extensive experiments have been conducted to improve the so-called G-suit which has long been part of the equipment of a combat pilot. This has made the pilot less sensitive to load-factor increases but before this invention has not been capable of protecting against G-LOC. Solutions have also been sought through over-pressure respiration and with the administration of a special gas in the oxygen system but these approaches have not provided a satisfactory solution.
In a current American research program efforts have been made to provide a method and a system for indicating purely physiologically that the pilot is tending toward loss of consciousness. Here the concept is to use sensors attached to the pilot's head to measure the blink frequency of the eyes, the activity in the brain or other values that can reveal if the normal conscious state is becoming critical. The method implies that these measuring data are processed and evaluated in a computer. In addition to it being very difficult to predetermine with certainty the limit when the critical state is reached for a particular pilot, the method also entails an increase in complexity from a technical system point of view with respect to the aircraft and its serviceability.
For the purpose of obtaining a simpler type of consciousness control it has further been suggested to introduce devices that sense the force with which the pilot grips the control stick and which, incorrectly, has been thought to quickly cease in the critical situation. Closely related is the concept mentioned in the specialist press of analyzing the frequency and character of the pilot's control stick movements in order to determine through such analysis whether the movements are logically correct in the prevailing flying situation. However, to attempt in this manner to distinguish normal control stick movements from the movements that the same pilot would be expected to perform if he has lost or is beginning to lose consciousness would be very difficult. Uncertainty due to individual differences between pilots is inevitable. Further, it seems impossible to provide a warning system based on frequency analysis which would work so quickly that a critical condition of the pilot can be detected and counteracted before it is too late. As mentioned above, in the case of G-LOC it is a matter of mere seconds before loss of consciousness occurs. This permits an extremely narrow time margin for a warning system to decide whether the pilot's condition is normal or abnormal on the basis of an evaluation of steering performance.
There is a similar risk to operators of land vehicles. Here, naturally, loss of consciousness due to high acceleration or acceleration growth does not occur, but a large number of accidents do occur which cannot be explained other than by the operator having fallen asleep. The reason is presumed to be that operation has become too tiring and monotonous and no apparatus has warned the operator before consciousness is lost.
Since the steering performance of a car driver at incipient loss of consciousness would be analogous to that of the pilot, the solution sought for flying should also be capable of solving the problem of lessening the risk of this type of car accident.
Despite the fact that the seriousness of the loss of consciousness problem has been known by experts for many years, and despite large efforts to provide a solution, no satisfactory solution to the problem has been presented.